Alberta Bianchin is an Associate Professor in the Planning Department at University Iuav of Venice (Italy), where she teaches cartography and associated new technologies (Gis and RS). Her research is focused in the Theory of Cartography, and New Technologies in Cartography, involving Remote Sensing and Geographic Information Systems. E-mail: .
THEORETICAL CARTOGRAPHY ISSUES IN THE FACE OF NEW REPRESENTATIONS
Alberta Bianchin
Planning Department University Iuav of Venice
Abstract
It can be argued that today's cartography includes 4 types of representations: graphic maps, photo-maps, satellite maps and GISs, the characteristic of which are herein defined. The similarities and differences of these documents are discussed from several points of view: the duality of the representational plane, the nature of media, the message context in the communication process, and the semiotic approach. Aerial photos and satellite images are then compared with graphic maps.
Premises
This paper takes for granted that today's cartography includes various types of maps. Many kinds of image-documents, be they analogue or digital, are available and are often proposed in place of traditional graphic maps.
In the last fifty years, the national mapping agencies have been proposing cartographic documents - photo or satellite maps - that use photographic expression in place of, or together with, the traditional map. In turn, the graphic map, by now digital and numerical, is done through Geographic Information Systems (Bianchin 1993).
Computer science's capacity to overcome the incompatibility between raster and vector formats has made it possible to integrate cartographic layers (vector) with ortho-photographic documents, resulting in what is called BD-ortho. As such, several products are now available in cartography. I find it useful to classify them in the following four typologies, the characteristics of which can be defined by basic descriptors referring to the physical principles of the technique and the signifier used, the system of signs, the kind of data recorded, the ideology underlying the specific technology, and any other characteristic related to their use.
· Graphic map
linear drawing _ geometry (point, line, polygon)
isolated objects _ selection between what is significant and what is not _ monosemic context
· Aerial photo
grain of photographic emulsion _ spots _ darkening of grains = light radiating from the surface
cover _ pansemic/polysemic context_need for discretization _ search of signifiers_ interpretation
· Satellite image
Raster _ grid+digital number (pixel) _ radiometric values
cover _ visualization and image processing
· GIS
vector _ geometry (point, line, polygon)
isolated objects _ selection between what is significant and what is not _ monosemic context
This initial description clearly identifies the elements shared by graphic maps and GISs and by aerial photos and satellite images, as well the analogue/digital opposition of graphic maps and aerial photos versus satellite images and GISs. All four categories, however, are image-documents, material objects that are the result of production processes and systems of signs located on the image plane and, thus, of spatial systems of signs as defined by Bertin (1967).
Document, here, is defined according to Escarpit (1976, p.120):
"On définira donc le document, comme un objet informationnel visible ou touchable et doué d'une double indépendance par rapport au temps:
- synchronie : indépendance interne du message qui n'est plus qu'une séquence linéaire d'événements, mais une juxtaposition multidimensionnelle des traces
- stabilité : indépendance globale de l'objet informationnel qui n'est plus un évènement inscrit dans l'écoulement du temps, mais un support matériel de la trace qui peut être conservé, transporté, reproduit."
The cartographic plane
Cartography deals with spatial (or geographic=localized) information, its acquisition and/or production, management, elaboration, and communication. For J. Bertin this means spatial systems of signs; for GIS literature, it means geographic or spatial systems.
Both, however, share a common idea of system that refers to space: the bi-dimensional space of the image (Bertin) and the space of a geo-referenced system, which is geodetic and ultimately plane (GIS). It must be remembered, however, that, in the GIS approach, “system” refers to the way in which information is structured in the DB, and the coordinates can be viewed as an attribute; while, in Bertin, it is an “image system”. Both of these spaces are geometric spaces (point, line, polygon) and a space of coordinates.
Photography is based on geometric perspective and, as such, it is also a geometric plane – or, in general terms, a surface with a relative system of coordinates. The visual system through which we perceive the images also presupposes a plane (or surface) where the visual image is formed.
The geometric plane and the coordinate system associated to it are the elements that bring together these various types of cartographic representations. As J. Bertin emphasizes, the cartographic plane is a geometric plane with its metric properties but, at the same time, it is also a plane of meaning, which is continuous and homogenous. This duality creates a source of misunderstanding as only the geometric planes and not necessarily the planes of meaning coincide.
Representation and communication
Mac Eachren begins the first chapter of his book stating that "Cartography is about representation". In the preface he states that: "The representational nature of maps, however, is often ignored – what we see when looking at a map is not the word, but an abstract representation that we find convenient to use in place of the world. When we build these abstract representations we are not revealing knowledge as much as are creating it."
A map, be it geographic or topographic, is a representation of the world. A representation implies the existence of an underlying object, what semiology calls a referent. In this case, the referent is the territory or, as topographers prefer, the earth's surface. The history of cartography relates directly to the history of visions of the world.
In the past, maps were created on the basis of geographic knowledge, which was derived from philosophical speculations or travel accounts (as in the atlases of Buaches, Gastaldi, Ortelius, etc.) or, since nineteenth century, from observation and description. These descriptions were established by disciplines and their categories. A description requires naming, classifying, unifying/separating, establishing relationships, and drawing what words are unable to express. Undoubtedly, some geographic descriptions are rooted in their graphic/cartographic representation.
The cartographic document, therefore, results from of two components: ideology (content) and technology.
IDEOLOGY + TECHNOLOGY = DOCUMENT
The intertwining between these two components can be analyzed starting from the document itself, as indicated by semiotics.
J. Bertin has already spoken of the map's role in communication, referring implicitly to the theory of the information. Bertin's analyses of the suitability of graphic constructions are always based on their communicative effectiveness or, more precisely, on the complete correspondence between the addressed and the received message.
The monosemic character of the message, on which he insists, guarantees the unequivocal nature of the communication process. The monosemic context is ensured by the map's legend introducing the code through which it is to be read.
The communication schema of a graphic map and, in the same way, of a GIS, has, as input, precise information to transmit (territorial objects), which is already listed in the legend or the data dictionary of the GIS. In addition, the GIS's query allows users to select the recorded data that fit the required message and thereby to construct their own thematic map.
Graphic process vs photographic process
Semiotics, according to Hjelmslev, introduces the distinction between the content and the expression plane. They are independent planes whose semiotic relation is materialized in the text, which is the result on the manifestation plane, a semiotic object, a specific occurrence which can be analyzed. “According to the generative point of view, the process of producing a text can be thought of as a twofold passage from the deep structures towards the surface structures, in the view of their manifestation at the moment of semiosis.” (Marsciani, Zinna p. 32).
In the field of the cartography today, two types of expression planes are available: graphic and photographic. To analyze them, I will consider the various types of documents, with the aim of ascertaining the meaning processes that have been put in action, especially as far as the representational aspect is concerned.
The base element of graphic expression is the line, from which more complex figures are generated, classified by geometry as points, lines, and polygons. The vector model of digital images presents exactly the same 'conversion' from the deep level - the 'single vector' or a 'couple of coordinates' - to the superficial level - the 'open or closed polyline' - that is manifested in a specific configuration.
By its very nature, the map or representation of the earth's surface produced by this type of expression plane privileges edges, separations between spaces, or perimeters of spaces – briefly put, linear objects or linear configurations. The content that it manifests is pre-determined by the geographic description of the territory of which the traditional map is coeval. The cartographic space is populated by the isolated objects listed in the legend and by the contours that describe the morphology.
In as much as it is semiosis, the map manifests, first and foremost, the geometric aspects of the territory; it transforms the geographic or territorial categories in geometric configurations; it records the edges of the objects. They are lifted out of anonymity thanks to toponymy. On the representation plane, the territory is nothing but the sum and the distribution of isolated objects (Chrisman 1997) over the cartographic plane, which coincides with the earth's surface; isolated objects described through their geometric configuration with the exception of scale and corresponding cartographic rules.
The base element of the photographic expression plane is the spot (or perceptible or recordable minimal surface) that differs in contrast from adjacent spots. In analogue photography, it is an irregular photographic grain; in digital photography, it is a discreet element with regular geometry. The aggregation at a higher level is obtained by chromatic homogeneity and contiguity among spots. Each point of the image space is qualified by a chromatic value. The image displays colors or grey levels.
On the content plane, the territory that is rendered by an aerial photo is visual and is recorded through the properties of color, form, and dimension (Casati 1991). Thus, the same referent is declined differently in the content planes associated to the two expression planes.
It is worthwhile analysing the terms of the production process in both cases.
The graphic map records already defined geographic objects. It refers to an interpretation of the world previously constructed by disciplines such geography, morphology, agronomy, etc.. The objects have been selected by the cartographer and displayed on the map according to a graphic code listed in the legend. In the communication schema, the cartographer is the addresser; the reader of the map, the receiver. The user of the map can only receive selected information, which has been made completely clear by reading instructions. As far as the user is concerned, the cartographic process has already censored what is meaningful from what is not.
The aerial photograph records some of the world's visible properties; it makes a selection that depends on physical properties and phenomena regarding the territory, as well the technological characteristics of the recording system (photography or remote sensing). As previously mentioned, the observer receives color spots, which occupy the whole image space with continuity. Finding world objects or phenomena requires interpretation and categorization committed to the user.
Going back to Mac Eachren's definition of a map "[…] representation that we find convenient to use in place of the world", we might add that, while the traditional map proposes an abstract representation by creating it, the aerial photograph does so by revealing it. Both can be used in the place of the world.
The photographic vs the cartographic message
The message of the graphic map has been developed and studied, in general terms, by J. Bertin and, in a more articulate and comprehensive framework, by H. Schilchmann. As far as photographic communication (in this case photo-maps or aerial photos) is concerned, it is useful to refer to the essay in which R. Barthes qualifies the photographic message as non-codified, clearly expressing the difference between a graphic map, which displays discrete units, and the photographic continuum.
"Quel est le contenu du message photographique? Qu'est-ce que la photographie transmet? Par définition, la scène elle-même, le réel littéral. De l'objet à son image, il y a certes une réduction : de proportion, de perspective et de couleur. Mais cette réduction n'est à aucun moment une transformation (au sens mathématique du terme); pour passer du réel à sa photographie, il n'est nullement nécessaire de découper ce réel en unités et de constituer ces unités en signes différents substantiellement de l'objet qu'ils donnent à lire; entre cet objet et son image, il n'est nullement nécessaire de disposer un relais, c'est à dire un code ; certes l'image n'est pas le réel; mais elle en est du moins son analogon parfait, et c'est précisément cette perfection analogique qui devant le sens commun, définit la photographie : ainsi parait le statut particulier de l'image photographique: c'est un message sans code ; proposition dont il faut tout de suite dégager un corollaire important : le message photographique est un message continu."
In the cartographic context, this problem is well known. Photo-interpretation procedures and methodologies aim to find sign-units that seem to be consistent with the phenomenon studied. In remote sensing, classification procedures produce, on the bases of their radiometric properties, image-units to which territorial meanings are associated.
The realism of photography
The following summarizes the arguments that have been put forth to explain the realism of photography (Dubois, 1983).
1. The automatism of its technical genesis implicitly guarantees absolute mimesis, the perfect coincidence of the real object with its image. Comparison is usually made with the manual picture or drawing.
"Pictures produced by camera can resemble paintings or drawings in presenting recognizable images of physical objects. But they have also characteristics of their own, of which the following two are relevant here: first the photograph acquires some of its unique visual properties through the technique of mechanical recording; and second, it supplies the viewer with a specific kind of experience, which depends on his being aware of the picture's mechanical origin. To put it more simply: (1) the picture is coproduced by nature and man and in some ways looks strikingly like nature, and (2) the picture is viewed as something being by nature." (Arnheim 1974, p.156)